Effect of Distal Tibiofibular Syndesmosis Overcompression on the Biomechanical Properties of the Ankle Bones: An In Vitro Cadaveric Model

Abstract

Category: Trauma; Ankle Introduction/Purpose: Overtightening of the distal tibiofibular syndesmosis during open reduction and internal fixation (ORIF) of ankle fractures remains a clinical concern, and there are limited data delineating the effect of syndesmosis overcompression on subsequent range of motion of the ankle joint bones. The primary objective of the current study was to determine the effect of syndesmotic overcompression on the relative range of motion (ROM) of the tibia, fibula, and talus, and to determine the syndesmotic fixation construct that most accurately restores native motion. Methods: Ten cadaveric lower limbs were utilized (78.3±13.0 yrs, 4F; 6M). A musculoskeletal simulator at ±7.5 Nm was used to test flexibility in dorsiflexion-plantarflexion, inversion-eversion, and internal-external rotation. After intact testing, syndesmotic probes were used to arthroscopically measure the intact position of the distal tibiofibular syndesmosis. The force needed to compress the syndesmosis just beyond the intact position represented the intact force (100%), and overcompression was defined as 150% of the intact force. The anterior inferior tibiofibular ligament (AITFL), interosseus membrane (IOM), and posterior inferior tibiofibular ligament (PITFL) were then sectioned. Testing was repeated for destabilized, IOM reconstruction at 100% compression and 150% overcompression, IOM reconstruction plus AITFL fixation at 100% compression and 150% overcompression, and AITFL fixation alone. ROM data was reported as a percentage of the intact condition. Repeated measures ANOVA and Bonferroni post hoc test were performed to assess differences between conditions with p< 0.05. Results: Average force needed to compress the syndesmosis was 71.0 ± 22.2 N. There was a significant increase in distal tibiofibular ROM in internal and external rotation for all conditions compared to intact (Figure 1) (p < 0.05). In the axial plane, reconstruction of the IOM membrane did not restore the intact condition and was similar to the destabilized treatment, regardless of compression force. The addition of AITFL fixation significantly reduced distal tibiofibular motion compared to IOM reconstructions alone, but still did not approach the intact condition. Overcompression of the syndesmosis did not significantly affect relative ROM of the ankle bones in any plane (p>0.05). Changes in the proximal tibiofibular ROM were similar in magnitude and direction as the distal tibiofibular ROM for all conditions. Conclusion: In the current study, overcompression of the distal tibiofibular syndesmosis did not restrict relative ROM of the tibia, fibula, or talus. Reconstructing the AITFL in addition to the IOM decreased tibiofibular ROM, particularly in the axial plane. In the clinical setting, surgical reconstruction with dynamic fixation of the distal tibiofibular syndesmosis may result in increased ROM and mechanical stress at the proximal tibiofibular articulation.